A disk drive typically includes a number of magnetic disks mounted to a common spindle for rotation. Each magnetic disk surface has an associated head arm assembly which includes a head gimbal assembly. The head arm assemblies are generally attached to an actuator for positioning a transducer, which is joined to the head gimbal assemblies, with reference to data tracks on the magnetic disks. In an effort to make disk drives smaller, disk drive manufacturers want the space required for the head gimbal assemblies between adjacent magnetic disk surfaces to be as small as possible.
A head gimbal assembly is comprised of an air bearing slider on which a magnetic transducer is deposited. The slider is attached to a flexure which in turn is attached to a load beam. Transducer wires are connected to the transducer. The load beam exerts a force on the flexure/slider combination towards the surface of a disk. As the disk is rotated, an air bearing is created between the air bearing surface (ABS) of the slider and the surface of the disk which exerts a force on the head gimbal assembly away from the surface of the disk.
The transducer can be a inductive type transducer which requires two transducer wires or a magnetoresistive type transducer which requires four or more transducer wires. The transducer preferably is a thin film transducer which is deposited directly onto the slider. Over time the size of the slider has been reduced allowing the data track density on the magnetic disks to be increased thereby resulting in an increased storage capacity for a disk drive system having the same size magnetic disk. The slider size has decreased from a standard size, i.e., 0.160 inch long, 0.125 inch wide, and 0.0345 inch high, to a macro size (70% of standard), then to a nano size (50% of standard) and now to a pico size (25-35% of standard).
The stiffness of a wire is a function of the diameter, i.e. gauge of the wire and the length of the wire. As the wire length becomes shorter, the stiffness of the wire increases. As the diameter of the wire decreases, the resistivity of the wire increases resulting in a decrease in the signal-to-noise ratio, and the stiffness decreases for a given length of wire. Where a wire is bonded along the wire's length at several locations, the length of the wire defines the stiffness of the wire between two adjacent bonding points.
In the prior art, a transducer wire is attached to a bonding pad on the slider and to a point on the load beam. The stiffness of the transducer wire places stress on the bond between the bonding wire and the bonding pad, and adversely affects the freedom of movement of the flexure/slider combination and the overall flying characteristics of the slider. In order to reduce these adverse effects of the transducer wires on the head gimbal assembly, the prior art has increased the length of the transducer wires as much as possible to form a loop between the bonding point of the transducer wires on the load beam and the bonding pads on the slider. This loop is referred to as a service loop.
In a standard size slider, transducer wires used with inductive type transducers were commonly 44 gauge, had a wire diameter of 0.002 inch, and had a service loop length of 0.2 inch which yielded a relative stiffness of 0.5 for the two transducer wires.
In a nano size slider, the transducer wires used with inductive type transducers were commonly reduced to 48 gauge, a wire diameter of 0.0012 inch, and had a service loop length of 0.15 inch which yielded a relative stiffness of 0.36 for the two transducer wires.
However when a magnetoresistive type transducer with four transducer wires is used, the four transducer wires are made of 48 gauge, with a wire diameter of 0.0012 inch, and a service loop length of 0.15 inch. This results in the undesirable relative stiffness of 0.73 for the four transducer wires. To reduce the relative stiffness of the four transducer wires, the transducer wire size can be changed to 50 gauge, a wire diameter of 0.001 inch, and if the service loop length remains at 0.15 inch, the relative stiffness will be decreased to 0.36 for the four transducer wires. The increase in the gauge of the transducer wire will have the adverse effects of increasing the resistivity of the wire thereby decreasing the signal-to-noise ratio characteristic of the transducer wire and will decrease production yields because of the increased likelihood of damage to the thinner wires.
One wiring approach is for the four wires to be routed along the edge of load beam and bonded to the load beam at a bonding point near the slider. The wires then are directed over the top of the flexure to the transducer bonding pads. The size of the service loop is the wire length between the bonding point on the load beam and bonding pads. This routing of the four wires over the top of flexure has the adverse effect of increasing the spacing between adjacent magnetic disk surfaces thereby increasing the overall size of the disk drive.
Another wiring approach is for the four transducer wires to be routed along the edge of load beam. The transducer wires are divided into two groups wherein the first group of transducer wires is bonded to load beam at a point on one side of the load beam and the second group of transducer wires is bonded to the load beam at a point on the second side of the load beam. Each group of wires then forms a service loop along one side of the slider from the bonding point on the sides of the load beam to the bonding pads. This transducer wire routing has the advantages of decreasing the space between adjacent magnetic disk surfaces and the use of two service loops that aid in maintaining the stability and flying characteristics of the slider. This routing has the disadvantage of restricting how close the head gimbal assembly can come to the spindle because the service loops will be the first point of contact with the spindle thereby deceasing the number of usable tracks on each magnetic disk surface.
Another wiring approach is for the four wires to be routed along the edge of the load beam and bonded to the load beam at a point along the non-spindle side of the load beam near the slider. A service loop is formed by routing the transducer wires along the non-spindle side of slider from the bonding point on the load beam to bonding pads. This routing of the wires has the advantages of decreasing the space between adjacent magnetic disk surfaces and increases how close the head gimbal assembly can come to the spindle because a service loop will no longer be the first point of contact with the spindle. This routing has the disadvantage that the service loop will bias the slider on one side thereby adversely affecting the flying characteristics of the slider.